This invention relates to flexible heating elements, and in particular to flexible plastic heating elements.
Flexible plastic heating elements have been known for a number of years, and have been satisfactorily employed in a number of applications, particularly in heating elements for floors. These elements comprise an elongate web of an electrically conductive plastic, such as a polyethylene and carbon black mixture. There are electrodes embedded in the web, extending longitudinally adjacent each edge. These electrodes may be, for example, a braided wire. The electrodes allow a potential to be applied transversely across the web, thereby generating heat. There are a plurality of slots extending transversely across the web, to increase the flexibility of the web and decrease the cross sectional area of the web.
An example of this prior art heating element is the STEP WARMFLOOR.TM. heating element available from Electro Plastics, Inc., 1780 Beltway Drive, St. Louis, Mo. 63114. These heating elements are made from an electrically conductive butyl soluted low density polyethylene. These heating elements are typically installed on a layer of adhesive applied to the floor. An insulating layer is applied over the heating element, and then leveling compound used to level the floor before the finished floor covering, e.g., wood, tile, or carpet, is installed. These heating elements are becoming increasingly popular because they operate at relative low voltages (24 volts in most applications), and are to some extent self regulating because as the temperature of the element increases, the resistance increases, decreasing the current and thus the heat being generated. Moreover, the use of these heating elements in floors provides a more even heat distribution, greater comfort, less temperature stratification, better control and increased ability to provide zoning, and the elimination of forced air which can circulate dust and germs. Because the plastic heating element is electrically conductive, there have been some concerns that in some applications the heating element should be electrically insulated.
According to the heating element of the present invention, a flexible plastic heating element is provided with an electrically insulating coating of an adhesive, preferably a pressure sensitive adhesive, and most preferably a latex-based pressure sensitive adhesive. The adhesive not only secures the heating element to the substrate on which it is placed and secures the floor covering to the heating element, but it electrically insulates the element. Thus the improved heating element is ideally suited for use in floors where the adhesive secures the element to the substrate, and secures a covering, such as carpet or tile, to the element.
The improved flexible heating element of the present invention can be made quickly and inexpensively by coating a conventional plastic heating element with an adhesive. Removable protective sheeting can be applied over the top and bottom surfaces of the heating element to facilitate handling the heating element until it is installed, and to protect the insulating adhesive coating. The heating element of the present invention thus has all of the advantages of the prior art flexible plastic heating elements, with the added advantages of being electrically insulated and self-adhesive.